WEBVTT - Will Sharks Die If They Stop Moving? 0:00:01.920 --> 0:00:04.320 Welcome to brain Stuff, a production of I Heart Radio, 0:00:06.280 --> 0:00:10.760 Hey brain Stuff Lauren Vogel Bam. Here, sharks take doing 0:00:10.800 --> 0:00:13.680 the wave to a whole new level. They swim by 0:00:13.760 --> 0:00:17.319 waving their body inside to side curves. It starts with 0:00:17.360 --> 0:00:20.759 the head turning first one way, then another. The movement 0:00:20.840 --> 0:00:24.759 ripples down their torpedo shaped body, pushing the water away 0:00:24.880 --> 0:00:29.159 and providing forward propulsion. Last comes the tail, with the 0:00:29.200 --> 0:00:32.200 fins shaped to allow them to move quickly and achieve 0:00:32.280 --> 0:00:37.479 immense liftoff or propulsive downward thrust. Obviously, a shark has 0:00:37.520 --> 0:00:40.120 to swim to catch its prey, meet its mates, and 0:00:40.200 --> 0:00:43.360 avoid its predators. But does a shark have to swim 0:00:43.640 --> 0:00:47.199 just to stay alive. You may have heard that a 0:00:47.240 --> 0:00:50.480 shark will drown if it stops moving, an idea that's 0:00:50.479 --> 0:00:53.880 been sited everywhere from biology textbooks to Ripley's Believe it 0:00:53.960 --> 0:00:57.800 or not. This theory came about by comparing sharks, which 0:00:57.800 --> 0:01:02.160 are classified as cartilaginous fish, to bony fish, which have 0:01:02.320 --> 0:01:05.880 many more muscles around their breathing apparatus is the gills. 0:01:07.440 --> 0:01:10.959 To understand why this distinction is important, let's take a 0:01:11.000 --> 0:01:14.640 look at how sharks and other fish breathe. To breathe, 0:01:14.760 --> 0:01:18.679 sharks must remove oxygen from the water around them. The 0:01:18.760 --> 0:01:22.520 water enters the shark's mouth, its nose being used exclusively 0:01:22.560 --> 0:01:25.720 for smell, and then the water flows over the gills. 0:01:26.400 --> 0:01:30.600 Inside those gills, there are hundreds of feathery gill filaments. 0:01:30.600 --> 0:01:34.280 Each filament, in turn has thousands of leaf like lamellie 0:01:34.440 --> 0:01:38.399 or flaps, which contain blood vessels. The blood absorbs the 0:01:38.400 --> 0:01:41.759 oxygen from the incoming water, and the excess water flows 0:01:41.760 --> 0:01:45.720 back out of the shark's body through gill slits. Sharks 0:01:45.800 --> 0:01:48.680 have five to seven pairs of gill slits, depending on 0:01:48.720 --> 0:01:53.639 the species. Using this method, sharks can extract about eighty 0:01:53.680 --> 0:01:56.720 per cent of oxygen out of the meager one percent 0:01:56.800 --> 0:01:59.920 of free oxygen that's present in the water. To compare, 0:02:00.240 --> 0:02:02.080 the air that we breathe is made up of about 0:02:02.920 --> 0:02:09.320 available oxygen, but human lungs only extract about of that anyway, 0:02:09.360 --> 0:02:12.959 to maintain a steady flow, the shark constantly needs to 0:02:13.000 --> 0:02:17.120 be taking in water. But does it have to constantly 0:02:17.200 --> 0:02:20.680 swim to take in this water? A scientist's thought so, 0:02:20.919 --> 0:02:24.360 because other fish seemed to have the equipment to actively 0:02:24.440 --> 0:02:27.360 pump the water through their mouth and over their gill slits, 0:02:27.840 --> 0:02:32.120 whereas sharks looked less developed. But that doesn't account for 0:02:32.160 --> 0:02:34.960 sharks that just kind of chill, like angel sharks and 0:02:35.040 --> 0:02:38.360 nurse sharks. It turns out that not all sharks have 0:02:38.480 --> 0:02:43.200 to stay moving to breathe. The oldest sharks, the ancestors 0:02:43.240 --> 0:02:46.640 of more modern sharks, didn't have to constantly swim in 0:02:46.760 --> 0:02:50.360 order to breathe. Rather, they pumped water through their mouth 0:02:50.440 --> 0:02:54.560 and over their gills. This method is known as buckle pumping, 0:02:54.960 --> 0:02:57.840 named for the buckle or cheek muscles that pull the 0:02:57.880 --> 0:03:01.400 water into the mouth and over the gills. Many sharks 0:03:01.400 --> 0:03:04.680 retain this method today, such as the aforementioned nurse and 0:03:04.760 --> 0:03:07.960 angel sharks, as well as carpet sharks, eskates, and rays. 0:03:08.040 --> 0:03:11.639 The sharks cousins also breathe this way. These species tend 0:03:11.720 --> 0:03:14.160 to spend most of their time laying on the bottom 0:03:14.160 --> 0:03:18.680 of the ocean floor. Many of these sharks are dorso 0:03:18.800 --> 0:03:22.880 ventrally flattened, that is, sort of squashed looking along the 0:03:22.960 --> 0:03:26.919 length of their Backlike the angel shark, they have stronger 0:03:27.000 --> 0:03:30.160 muscles in the face. These sharks might also have a 0:03:30.160 --> 0:03:33.639 more prominent spircle, which is a tube behind the eyes. 0:03:34.320 --> 0:03:36.360 When a shark is buried at the bottom of the 0:03:36.360 --> 0:03:39.920 ocean floor and can't breathe through its mouth, the spircle 0:03:40.040 --> 0:03:44.040 can pull in water instead. As sharks evolved and became 0:03:44.040 --> 0:03:48.680 more active, however, buckle pumping became secondary. It was simply 0:03:48.840 --> 0:03:52.000 more energy efficient to take in water while swimming, in 0:03:52.080 --> 0:03:54.920 effect ramming the water into the mouth and letting it 0:03:54.920 --> 0:03:58.200 flow through the gill slits. This method of breathing is 0:03:58.280 --> 0:04:02.400 known as a ram ventilation. Most sharks can alternate between 0:04:02.480 --> 0:04:05.520 buckle pumping and ram ventilation depending on what they're doing. 0:04:06.040 --> 0:04:08.720 When they start swimming fast enough to force the water 0:04:08.760 --> 0:04:11.240 in more quickly than they could pump it, then they 0:04:11.360 --> 0:04:14.720 stop pumping. The sand tiger shark is an example of 0:04:14.760 --> 0:04:18.560 a shark that switches back and forth. Some sharks, however, 0:04:18.640 --> 0:04:21.880 have completely lost the ability to breathe by buckle pumping, 0:04:22.400 --> 0:04:25.040 and these are the sharks that will indeed drown if 0:04:25.040 --> 0:04:29.120 they stop swimming and thus ramming water. These sharks are 0:04:29.160 --> 0:04:33.719 known as obligate ram breathers or obligate ram ventilators, and 0:04:33.839 --> 0:04:36.880 only about two dozen of the four hundred identified shark 0:04:36.920 --> 0:04:41.520 species are required to maintain this forward swimming motion. These 0:04:41.560 --> 0:04:44.880 include the great white shark, the mako shark, the salmon shark, 0:04:45.000 --> 0:04:49.920 and the whale shark. So do these obligate ram breathers 0:04:50.040 --> 0:04:54.160 ever get a break? Aren't they tired? As it turns out, 0:04:54.360 --> 0:04:57.120 it's more work for these sharks to remain still than 0:04:57.160 --> 0:04:59.960 it is to swim. In a study of lemon shark 0:05:00.120 --> 0:05:04.440 switch switch between breathing methods, juveniles breathed six percent more 0:05:04.440 --> 0:05:08.440 efficiently when moving than when resting, even when resting so 0:05:08.480 --> 0:05:11.000 that the current allowed the water to flow directly into 0:05:11.000 --> 0:05:14.560 their mouths. That's not to say that these sharks don't 0:05:14.600 --> 0:05:17.719 catch a break every now and then. For obvious reasons, 0:05:17.800 --> 0:05:19.720 it can be hard to keep track of a shark 0:05:19.800 --> 0:05:23.360 that's constantly swimming, so it's difficult for scientists to know 0:05:23.600 --> 0:05:27.599 how or when they rest. An experiment with a small shark, 0:05:27.720 --> 0:05:31.520 the spiny dogfish, indicated that swimming is coordinated by the 0:05:31.560 --> 0:05:35.000 spinal cord, not the brain, so sharks may be able 0:05:35.040 --> 0:05:37.839 to shut down their brain and rest while still swimming. 0:05:39.320 --> 0:05:42.080 Sharks in needisome rest may also take advantage of the 0:05:42.120 --> 0:05:44.599 factors that affect the amount of oxygen in the water, 0:05:44.800 --> 0:05:48.320 such as salinity, temperature, and even the time of day. 0:05:48.720 --> 0:05:51.840 In the nineteen seventies, scientists investigated what came to be 0:05:51.920 --> 0:05:54.760 known as the Caves of the Sleeping Sharks in Mexico. 0:05:55.560 --> 0:05:59.200 Inside the caves were motionless reef sharks, which are normally 0:05:59.240 --> 0:06:03.760 obligate ventilators. The scientists determined that the water in the 0:06:03.800 --> 0:06:08.560 caves had an extremely high amount of oxygen and reduced salinity. 0:06:09.080 --> 0:06:12.400 These conditions likely made it easier for even these sharks 0:06:12.440 --> 0:06:16.320 to breathe without moving. They may not have been asleep 0:06:16.400 --> 0:06:19.320 like humans, their eyes were open, for one thing, but 0:06:19.440 --> 0:06:22.760 it does appear that sharks can get some rest, and 0:06:22.839 --> 0:06:25.599 many other reef sharks have also been observed motionless at 0:06:25.600 --> 0:06:29.800 the bottom even outside of caves. Scientists still aren't exactly 0:06:29.880 --> 0:06:37.960 sure how they can do this. Today's episode is based 0:06:37.960 --> 0:06:40.760 on the article will a shark drown if it stops moving? 0:06:40.880 --> 0:06:44.160 On how stuffworks dot Com, written by Molly Edmonds. Brain 0:06:44.200 --> 0:06:46.360 Stuff is production of I Heart Radio in partnership with 0:06:46.400 --> 0:06:48.960 how stuff works dot Com and is produced by Tyler Klang. 0:06:49.400 --> 0:06:52.080 Four more podcasts my heart Radio, visit the i heart 0:06:52.120 --> 0:06:54.960 Radio app, Apple Podcasts, or wherever you listen to your 0:06:54.960 --> 0:06:55.680 favorite shows.